A much-trumpeted partnership of one of today's most celebrated scientists and the world's largest publicly traded oil company seems stalled in its aim of creating mass-market biofuel from algae, and may require a new agreement to go forward. The disappointment experienced thus far by scientist J. Craig Venter and ExxonMobil is notable not only because of their stature, but that many experts think that, at least in the medium term, algae is the sole realistically commercial source of biofuel that can significantly reduce U.S. and global oil demand.

Venter, the first mapper of the human genome and creator of the first synthetic cell, said his scientific team and ExxonMobil have failed to find naturally occurring algae strains that can be converted into a commercial-scale biofuel. ExxonMobil and Venter's San Diego-based Synthetic Genomics Inc., or SGI, continue to attempt to manipulate natural algae, but he said he already sees the answer elsewhere -- in the creation of a man-made strain. "I believe that a fully synthetic cell approach will be the best way to get to a truly disruptive change," Venter told me in an email exchange.

Venter made his remarks before a conference this week on the future of energy at the New America Foundation in Washington, D.C., and in subsequent emailed replies to questions.

A drive to reduce dependence on fossil fuels -- because of vulnerability to the volatile Middle East, concern about global warming, and the hundreds of billions of dollars spent on oil imports -- lies behind such efforts to create a scaled-up biofuel. Since up to half of algae is already oil in its natural state, many experts say it is a superior alternative to biofuels created from agricultural products such as corn, palm and switchgrass, which contain much smaller percentages of oil.

When announced in July 2009, the Venter-ExxonMobil alliance of colossals attracted wide publicity. It called for ExxonMobil to spend up to $600 million if publicly undisclosed milestones were reached in the lab. The Wall Street Journal said the partnership might signal "a coming of age" for algae biofuel. Greenbang fretted that the alliance might actually prove "unholy," but not Gigaom, which said it could be "algae's big break."

The terms of the alliance omit the fully synthetic approach that Venter is now advocating, so he is conducting "an ongoing dialog" with Exxon about a new agreement, he said. He appeared to suggest that such a new compact would require more Exxon investment.

ExxonMobil spokesman Alan Jeffers suggested that the company has a different assessment of the alliance's state of play. "The ExxonMobil-SGI algae project is ongoing and has reached no such conclusions as characterized in your note," Jeffers told me in an email. (I had asked whether it is true that the alliance had failed to find a suitable strain of natural algae, and that Venter was seeking to shift to a new stage of research.).

What we may be witnessing is simple friction between the well-known conservative ways of Exxon and the free-wheeling, iconoclastic Venter. In this case, Venter from the outset may have wanted to move directly to the test-tube and create his own algae, while Exxon -- holding the purse-strings -- advocated a less-expensive, step-by-step approach starting with existing strains. There is no sign of anything approaching a rupture. But if the alliance does eventually fail, it would be a serious blow for Venter, who has said that to succeed he needs access to the deep pockets of a Big Oil company, and to a significant but lesser degree for ExxonMobil, which has widely promoted the partnership as evidence that it is a forward-looking company